Advanced sequential batch gasification process

ABSTRACT

The invention relates to a two stage process for the thermal treatment of wastes consisting of a batch gasification process followed by a syngas combustion process. A system and method are provided comprising of one or more first process stage batch gasification chambers ( 1 ) which are connected to a common second process stage chamber, the syngas combustion chamber, or alternatively a syngas conditioning chamber ( 13 ) and afterwards a combustion of the syngas in either a combustion chamber, reciprocating engine, boiler, gas turbine or an internal combustion device. The process can also be used to process biomass and fuels by gasification. The gasification chamber ( 1 ) has separated nozzle areas corresponding to plenum sections of the bottom where a mixture of air and recirculated flue-gas ( 8 ) is blown under the combustible material. Flue gas flow is regulated by varying the production of syngas in the gasification chambers ( 1 ) by a feedback signal from devices such as draught sensors, thermocouples, fan speeds indicators, steam flow meters, oxygen concentration meters and power production indicators.

FIELD OF THE INVENTION

The present invention relates to an Advanced Sequential BatchGasification Process for the thermal treatment of waste and applicationsto use such process for waste destruction and energy generation. Theinvention can also be used for the gasification of biomass and otherfuels to produce useful energy.

BACKGROUND OF THE INVENTION

It is a known art to use a two stage combustion process to burncombustible waste materials under substoichiometric conditions (starvedair conditions). In this kind of process burn down of the waste takesplace in a first chamber resulting in combustible gas and ash, where thegas is further mixed with air and combusted under super stoichiometricconditions (excess air conditions) in the second chamber. It is also aknown method to use multiple first stage chambers with a common secondstage chamber.

WO 2008/068781 discloses a system and a method for oxidation of wastematerials. A set up of one or more gasification chambers, which areconnected via ductwork to a combustion chamber, are used to burn thewaste material. The waste is loaded into the gasification chamber(s) andignited there and the gas, which is generated by the substoichiometriccombustion in the gasification chamber, is fully combusted in thesecondary combustion chamber at a very high temperature. Waste is burneddown in a gasification chamber by providing a first stream of air flowfrom the bottom of chamber and is directed underneath and through thewaste. A second stream of air flow is then provided from the top of thefirst chamber. Thereafter, a combustion step takes place in a combustionchamber, where the gas produced in the gasification chamber is exposedto high temperature. The flow of gas/air exiting the second chamber thendetermines the speed of air flow from the bottom inlet in the firstchamber, to maintain constant flow of hot gases from the combustionchamber.

GB 2475889 discloses an apparatus for processing waste material andorganic materials such as biomass having a processing chamber forprocessing said material at an elevated temperature, in an oxygendeficient environment, to produce syngas and a combustion chamber forcombusting syngas. The apparatus further comprises a conduit meansbetween said combustion chamber and said processing chamber for carryinghot exhaust gasses from the combustion chamber to said processingchamber and a mirror arranged to reflect and concentrate sunlightthereby to cause the temperature within said processing chamber to beraised. The apparatus also comprises an injector means for introducingoxygen or oxygen containing gas into said combustion chamber to enablecomplete oxidisation of the syngas.

One of the problems of the prior art methods is control of the burn downphase in the gasification chamber. Due to complications with loadingwaste into the gasification chambers, distribution of the waste in thechambers is generally such that the load is lighter in the corners thanit is in centre of the chamber. This is simply due to the bulkiness andnon-homogeneous; particle size, shape and density. Flow of gas and/orair under the waste flow a path with the least resistance, which canresult in by-passing the bulk of the waste flowing up in the chambercorners rather than through the waste batch. This results in increasedexcess air combustion producing fully combusted flue-gas rather thangasification producing energy rich syngas. Moving the waste around inthe chamber during the gasification process to solve the above problemonly results in other problems related to carryover of dust particles tothe down-stream process.

SUMMARY OF THE INVENTION

The invention is an Advanced Sequential Batch Gasification Process,which has two main process stages. The first process stage consists ofone or more gasification chambers, while the second process stageconsists of a syngas combustion unit, such as a combustion chamber, oralternatively the syngas is routed to a boiler, gas turbine,reciprocating engine or other internal combustion device, with orwithout the use of a syngas conditioning chamber to condition the syngasbefore combustion.

Although the process can be used with only one gasification chamber forthe gasification of waste, biomass or other fuels, such a setup will notallow for a sequential process. For sequential operation and productionof an uninterrupted stream of syngas by gasification more than onegasification chamber is needed in the same system. When run withmultiple gasification chambers, sequentially, the gasification processcan produce a constant flow of syngas which enables continuousproduction of useful energy, for example electricity.

Multiple gasification chambers are run in sequence, such that at anygiven time, one or more chambers are producing syngas from waste,biomass or other fuel with gasification, while one or more chambers arecompleting the gasification process and other chambers are offline readyto be initiated for gasification or being discharged of ash and reloadedin preparation to process another batch of waste.

The problems stated above related to waste loading and the flow ofair/gas introduced into the gasification chambers are solved as follows.Each gasification chamber has a hearth with multiple nozzles at thebottom of the chamber. The nozzles penetrate through the hearthstructure forming a number of small openings between the hearth top andbottom surfaces. The volume under the hearth has plenums, which separatethe hearth nozzles into nozzle areas corresponding to the plenums havinga shape and number defined in the volume under the hearth. Recirculatedflue-gas and atmospheric air enter the bottom plenums via separate splitductwork system in which every branch has its own remotely controlledvalve for each plenum section with an independent control mechanism.Each plenum section is therefore provided with separate control forrecirculated flue-gas and atmospheric air respectively. This featureallows full control of recirculated gas and air flows into each nozzlearea (plenum section) and when during the process the system is feedeither atmospheric air or recirculated flue-gas or a mixture of both inany mixture ratio and flow rate at any time during the process,independently controlled in each plenum section.

With this system the nozzles in the centre of the hearth can be fedseparately with recirculated flue gas while other plenum sections areclosed off and then, when the bulk of the batch has been consumed by thegasification, the periphery of the bottom area and corners are also fedwith recirculated flue-gas. At the end of the process, atmospheric aircan be feed via all nozzles in the hearth to produce quality ash withpractically no carbon content.

In a first aspect of the present invention a process for thermaloxidation of combustible materials is provided. The process comprisesthe steps of gasification of combustible materials in one or moregasification chambers, transferring syngas from the one or moregasification chambers to a combustion unit, and combustion of syngasfrom the gasification chamber(s) in the combustion unit. The process ischaracterised in that external air, recirculated flue-gas from thecombustion unit or a mixture thereof is blown under different areas ofthe bottom of each gasification chamber at different times of agasification process via plenums and nozzles. This process is controlledby an industrial computer.

In a second aspect of the present invention an apparatus for thermaloxidation of combustible materials is provided. The apparatus comprisesone or more gasification chambers for gasification of combustiblematerials, where the one or more gasification chambers further comprisesinlets at the bottom of the chamber and one or more burners. Theapparatus further comprises a combustion unit for combustion of syngasfrom the first chamber, where the second combustion unit furthercomprises one or more gas inlet for receiving syngas from the one ormore gasification chambers, one or more burners, an inlet forrecirculated flue-gas diverted from the system exhaust stack, an inletfor atmospheric air and an outlet for disposing of flue-gas from thecombustion unit.

Thirdly the apparatus comprise a duct to transfer syngas from each ofthe gasification chambers to the combustion unit, the duct furthercomprising a valve to isolate each of the gasification chambers from thecombustion unit. Furthermore the device comprises a duct forre-directing flue-gas from the outlet of the combustion unit into theone or more gasification chambers and an industrial computer. Theapparatus is characterised in that the outlets at the bottom of eachgasification chamber are distributed across the bottom of the chamberand connected to duct for re-directing flue-gas from the outlet viaplenums and nozzles, such that air, flue-gas or a mixture thereof in anyratio is blown under different areas of the bottom of each gasificationchamber at different times of the gasification cycle phase.

DESCRIPTION OF THE INVENTION

The following embodiments and definitions relate to the process and theapparatus of the invention.

First process stage: Consists of one or more batch gasificationchambers.

Second process stage: Is for the combustion of the syngas. This can bedone either in a syngas combustion chamber or in an internal combustiondevice such as a gas turbine or a reciprocating engine, with or withoutthe use of a syngas conditioning chamber in which the syngas can bemixed for consistency before flowing to the combustion device andrelated systems.

Syngas: Consists primarily of hydrogen, carbon monoxide, methane andvarious hydrocarbons and very often some carbon dioxide the gas iscombustible and often used as a fuel for internal combustion engines.The energy density (heat value) of the gas and chemical composition canvary significantly. Impurities in the gas may need to be removed beforeit is combusted in a reciprocating engine or gas turbine. Theseimpurities may be among other; hydrogen chloride, sulphur dioxide, saltsand particulate matter. The concentrations of the impurities in thesyngas depend on the composition of the waste or fuel material processedby the gasification process.

Air: Is a colourless, odourless, tasteless, gaseous mixture, mainlynitrogen (approximately 78%) and oxygen (approximately 21%) with varyingamounts of moisture and particulate matter, enveloping the earth; theatmosphere, atmospheric air, ambient air.

Combustion air: Is the same as the above definition of Air, but usedspecifically for the purpose of combusting syngas or any type ofcombustible fuel.

Cooling air: Is the same as the above definition of air, but usedspecifically for the purpose of cooling equipment devices and equipmentcomponents.

Flue-gas: The product of complete chemical reactions of combustion ofsyngas and other combustible fuels with air (as the above definition ofair) and to a lesser degree recirculated flue-gas (as per the belowdefinition of recirculated flue-gas). The oxygen concentration influe-gas is typically 3-11%.

Recirculated flue-gas: Is the same as the above defined flue-gas butspecifically diverted from the system exhaust stack to be used forspecific purposes in the gasification system process.

Gas/air mixture: Is a mixture in any ratio of recirculated flue-gas asper the above definition and air as per the above definition.

The following embodiments disclose systems having one or more chambersof the first process stage (gasification chambers) connected viaductwork to a second process stage chamber (a syngas combustion chamberor a syngas conditioning chamber). The waste material, fuel or biomassis loaded into the gasification chamber(s) and ignited there.

The syngas generated by the gasification flows to the syngas combustionchamber and is combusted there for the production of flue-gas for anenergy recovery system.

The system is controlled by an industrial control computer to whichvarious instruments and equipment is connected, such as; thermocouples(thermometers), fan speed controls, burner controls, valve actuators,pressure sensors, limit switches, oxygen sensors and many other devisesused for input signals and controlled output signals.

In an embodiment of the present invention the combustible materialscomprise waste, fuel or biomass.

In an embodiment of the present invention the combustion unit is acombustion chamber, reciprocating engine, boiler, gas turbine or aninternal combustion device.

In an embodiment of the present invention the flow of fully combustedflue gas from the combustion unit is regulated by varying the productionof syngas in the one or more gasification chambers by a feedback signal.

In an embodiment of the present invention the combustion unit is acombustion chamber. In such embodiments the feedback signal is a signalfrom a steam flow meter, a meter of power output, speed indicator fromthe ID fan, flow signal from the outlet of the combustion unit or acombination thereof.

In an embodiment of the present invention the combustion unit is areciprocating engine, boiler, gas turbine or an internal combustiondevice. In such embodiments the feedback signal is a measure of thepower output of the reciprocating engine generator set, power output ofthe gas turbine generator set, or steam flow output from the boiler thatthe syngas is combusted in, where the output is proportional to the flowof syngas to the respective combustion unit.

In an embodiment of the present invention the device is set up such thata syngas conditioning chamber is connected to the one or moregasification chambers and the syngas is directed through ducts to thesyngas conditioning chamber from the one or more gasification chambersto mix the syngas from the one or more gasification chambers before itis routed to the combustion unit. The one or more gasification chambersare then connected to the combustion unit with ducts. The syngasconditioning chamber is used as a part of the second process stage tomix the syngas from the multiple gasification chambers to provide aconsistent quality of syngas to the second process stage combustion,where the syngas combustion takes place in a boiler, reciprocatingengine, gas turbine or internal combustion device. The syngasconditioning chamber is an insulated chamber in which the various flowsof syngas from the multiple gasification chambers are given some time tomix to produce a consistent mixture of syngas, without the addition ofany oxygen containing gases.

Syngas from the gasification of waste materials, fuels or biomass,containing little or no salts, chlorine, sulphur, acidic compounds,heavy metals or other impurities can be routed directly via manifold forcombustion to a boiler, gas turbine, reciprocating engine or otherinternal combustion device without conditioning in a conditioningchamber.

In an embodiment of the present invention where the combustion takesplace in a boiler, reciprocating engine, gas turbine or internalcombustion device the syngas flows from the two or more gasificationchambers is mixed to form a uniform quality of syngas with or withoutadditional syngas cooling, purification and/or cleaning beforecombustion.

Syngas containing elevated levels of impurities such as sulphurcompounds, hydrogen chloride, salts or other need to be conditioned andcleaned. After the conditioning chamber as described above the gaseswill enter a recovery boiler to cool the gas then the gas goes to awater-quench vessel where multiple high pressure water nozzles willspray water to mix with the syngas and dissolve the impurities, thesyngas may also be directed directly to the quench vessel. The watermoisture and droplets are removed from the syngas in a moistureseparator. The impurities are removed from the quench water byneutralization and filtering, alternatively the syngas can be filteredthrough a dry filtration system. The syngas flows on from the moistureseparator or alternative dry filtrations system to a boiler,reciprocating engine, gas turbine or other internal combustion devicefor combustion or alternatively the syngas can be further processed intoliquid fuel by Fischer-Tropsch process or other processes turninggaseous fuels into liquid fuels.

In an embodiment of the present invention the flow of the external airand the recirculated flue-gas in each plenum section area is regulatedindependently in each plenum section area such that at any given timemixture ratio of recirculated flue-gas and external air can be differentfrom one section area to the next. This is done by varying the level ofopening of each of the valves on the ducts between the recirculatedflue-gas and the external air fans respectively to the plenums in thevarious areas of the hearth.

In an embodiment of the present invention the overall flow of air andrecirculated flue-gas to the hearth sections is collectively regulatedby controlling the speed of the fans respectively such that at any giventime the overall flow of gas/air mixture is controlled with a feedbacksignal to control the rate of the syngas production.

In an embodiment of the present invention the one or more gasificationchambers are surrounded by a cooling jacket compartment(s) for coolingthe gasification chamber. In such embodiments air, water, thermal oil orother fluid are used as cooling media in the cooling jacketcompartment(s). When the gasification chambers are cooled by coolingmedia such as air, water, or other cooling fluid or a combination of anyof these with a cooling jacked compartment on the chambers, cooling thechamber walls, ceiling, bottom and syngas exit duct as needed bycontrolled flow of the cooling media. In the case of air cooling thecooling air can be used as pre-heated combustion air in the syngascombustion chamber or other use where there is need for warmed air. Inthe case of water cooling the primary chamber cooling jacketcompartment(s) can be used to preheat boiler water or any other usewhere there is need for heated water. An example of other cooling fluidsis heating oil which is in some cases used in closed circuit turbinesystems and/or utilising thermal oil as working media for industrial orspace heating purposes.

In an embodiment of the present invention the mixture of external airflow and recirculated flue-gas mixed in any ratio is introduced into thecombustion unit for the combustion of syngas. In such an embodiment theexternal air flow introduced into the combustion chamber is heated airfrom the cooling compartment of the gasification chamber.

In an embodiment of the present invention the flow of fully combustedflue gas is regulated by varying the production of syngas in the one ormore gasification chambers by a feedback signal from devices such as,but not limited to draught sensors, thermocouples, fan speed indicators,steam flow meters, oxygen concentration meters and power productionindicators.

In an embodiment of the present invention the gas/air mixture flow intothe two or more gasification chambers is independently controlledbetween the gasification chambers. In this embodiment the gas/airmixture flow from the bottom of the first process stage chamber(s) isindependently controlled.

In an embodiment of the present invention a controlled ratio of themixture of air and recirculated flue-gas flow is introduced under thewaste batch in the gasification chamber via plenums and nozzles whichare separated into areas and sections, where the air and recirculatedflue-gas ration can be controlled independently in each plenum sectionand blown through corresponding nozzles into the gasification chamber.The gasification chamber bottom structures have internally structuredgas/air plenums which are divided into several sections where eachsection covers a part of the bottom hearth area, each area have a set ofnozzles which penetrate from the plenum through the hearth into thechamber under the waste. By this arrangement the air and flue-gas flowsand mixture ratio can be individual controlled in each hearth section.There are no particular limitations to the area size, shape or number ofsections in each chamber, although 9 sections (3×3) in each chamber maybe a preferable division due to the ability to specifically control thecorners, sides and the centre areas of the chamber hearth independentlyof each other. Other preferable options of division may be 12 sections(3×4) or 16 sections (4×4) in each chamber. Other divisions may form twodimensional areas such as an inner (centre) area and an outer(peripheral) or surrounding area.

The waste load is generally lightest in the corners and heaviest in thecentre of the chamber simply due to the bulkiness of the waste and thecomplications of loading material which is not of homogeneous shape,size or density into a cuboid shaped void in a chamber with a rectangleshaped opening on top for loading, even a cylindrically shaped chamberwould have similar problems.

The intensity of the air and recirculated flue-gas flow under thevarious plenum sections areas under the waste batch is very important toensure production of high heat value quality syngas, rather than fullycombusted flue-gas. If the same flow intensity is used throughout thewhole bottom hearth plenums area through the whole operation sequencethe mixture of air and recirculated flue-gas can by-pass the waste batchby flowing from the nozzles in the chamber corners and flow around thewaste batch rather than through the batch. If this happens more fullycombusted flue-gas will be produced by excess air combustion rather thanhigh heat value syngas produced by gasification.

In an embodiment of the present invention where the combustion takesplace in a combustion chamber a gas/air mixture is introduced into thecombustion chamber for the combustion of syngas.

In an embodiment of the present invention where the combustion takesplace in a combustion chamber a flow of syngas, external air andrecirculated flue-gas into the entry end of the combustion chamber isautomatically controlled to ensure a controlled residence time,temperature and the final oxygen concentration of the flue-gas.

In an embodiment of the present invention the flow of flue-gas exitingthe combustion chamber determines the flow rate of the gas/air mixtureflow through the bottom plenums and nozzles under the waste batch in thefirst process chamber and therefore determines the rate of the syngasproduction.

In an embodiment of the present invention where the combustion takesplace in a combustion chamber the combustion of syngas in the combustionchamber is performed at a pre-set desired temperature and at acontrolled pre-set flow rate. Controlled flow of combustion air isprovided to the second process stage chamber. A controlled flow ofrecirculated flue-gas is also provided to the second stage processchamber at the same entry point as the combustion air. This recirculatedflue-gas is used with the combustion air to complete the combustion ofthe syngas from the first process stage chamber(s) and control the finaloxygen concentration in the flue-gas from the second process stagechamber. In this embodiment the gas and air mixture from the bottomplenum and nozzles under the waste in the first process stage chamber(s)is independently controlled, and then the flow of syngas from the firstprocess stage chamber flowing into the second process stage chamberregulates the flow of flue-gas from the second process stage chamber.

In an embodiment of the present invention a syngas manifold is used toroute the syngas flowing directly from the multiple gasificationchambers to the second process stage, where the syngas combustion takesplace in a boiler, reciprocating engine, gas turbine or internalcombustion device.

In an embodiment of the present invention where the combustion takesplace in a boiler, reciprocating engine, gas turbine or internalcombustion device the power output of the boiler, reciprocating engine,gas turbine or internal combustion device determines the production ofsyngas generated in the gasification chamber(s) by a feedback signal.

In an embodiment of the present invention where the combustion takesplace in a boiler, reciprocating engine, gas turbine or internalcombustion device the power output of the boiler, reciprocating engine,gas turbine or internal combustion device determines the flow rate ofgas/air mixture flow through the bottom plenums and nozzles under thewaste batch in the gasification chamber(s).

In an embodiment of the present invention the gas/air mixture flow fromthe bottom plenum and nozzles under the waste in the first process stagechamber(s) is independently controlled in each first stage chamber. Afirst stage chamber which was started first will have progressed intothe gasification process and will therefore have higher flow of gas/airmixture flowing under the waste than the chamber which was startedlater. The gasification progresses has increasing need for gas/airmixture as the lighter chemical compounds (higher hydrogen content) willbe consumed by the gasification sooner than the heavier compounds(higher carbon content). Therefore, at any given time the gas/airmixture flow may be for example at about ¾^(th) the maximum flow in onechamber while the next one will be at about ¼^(th) the maximum flow butboth would idle up and down in parallel motion depending on the need forsyngas flow. Then the flow of syngas from the first process stagechamber flowing into the second process stage chamber regulates the flowof flue-gas from the second process stage chamber.

In an embodiment of the present invention the oxygen concentration ofthe external air and the recirculated flue-gas mixture in each plenumsection area is regulated independently by such that at any given timemixture ratio of recirculated flue-gas and external air can be differentfrom one section area to the next. This is done by varying the level ofopening of each of the valves on the ducts between the recirculatedflue-gas and the external air fans respectively to the plenums in thevarious areas of the hearth.

The gas/air plenums are fed with a controlled flow of atmospheric air orrecirculated flue-gas, or a mixture of both in a controlled ratio. Therecirculated flue-gas is diverted from the process exhaust stackductwork and mixed with atmospheric air on the entry in to the plenums.Controlled and lowered concentration of oxygen reduces the production ofnitrogen oxides. Also, the use of hot mixture of air and recirculatedflue-gas with lower oxygen concentration for the gasification; produceshigher heat value syngas than using colder and higher oxygenconcentration such as atmospheric air.

Three independent control features are provided for the mixture of airand recirculated flue-gas which is fed through the nozzles in the bottomhearth under the waste batch. These are:

-   -   Control of oxygen concentration (mixture ratio) of the air and        recirculated flue-gas mixture independently in each plenum        section area    -   Control of air and recirculated flue-gas mixture flow        independently to individual plenum section area    -   Control of overall flow of air and recirculated flue-gas mixture        to the hearth sections collectively

The whole process is controlled by means of industrial computercontrolling gas and air flow rates with remotely controlled valves,fans, burners and other instruments with respect to various feedbacksignals from the process such as draught sensors, thermocouples, fanspeeds indicators, steam flow meters, oxygen concentration meters andpower production indications.

The total combined flow of syngas from all chambers governs theproduction and flow of fully combusted flue-gas flowing from the syngascombustion chamber. This flow of flue-gas is controlled and maintainedat a consistent flow rate which is extremely important for efficientrecovery of useful energy and effective emissions control. The flow ofthis fully combusted flue gas is controlled by varying the production ofsyngas in the gasification chambers and the production of syngas isvaried by increasing or decreasing the flow of air and recirculated fluegas mixture blown through the air/gas plenums and nozzles under thewaste batch in the gasification chambers.

The feedback signal used for this can be of a few different types, inthe case of utilizing the syngas in a syngas combustion chamber andrecovery boiler the following can for example be used as feedbacksignals:

-   -   The power output of a steam turbine generator system which is        proportional to the steam flow from the boiler, which again is        proportional to the flow of flue-gas from the syngas combustion        chamber.    -   Steam flow meter signal which is proportional to the flow of        flue-gas from the syngas combustion chamber.    -   Speed indication of ID fan which indicates the total flow of        flue-gas from the syngas combustion chamber.    -   A measure of the flow of flue-gas flowing from the syngas        combustion chamber

In the case of utilizing the syngas in a reciprocating engine, gasturbine, boiler or other internal combustion device, the following canfor example be used as feedback signal:

-   -   The power output of the reciprocating engine generator set,        which is proportional to the flow of syngas to the engine.    -   The power output of the gas turbine generator set, which is        proportional to the flow of syngas to the gas turbine.    -   The steam flow from the boiler that the syngas is combusted in.        The steam flow is proportional to the flow of syngas to the        boiler.

The waste load is generally lightest in the corners and heaviest in thecentre of the chamber simply due to the bulkiness of the waste and thecomplications of loading material which is not of homogeneous size,shape and density into a cuboid shaped void in a chamber with arectangle shaped opening on top for loading.

The intensity of the air and recirculated flue-gas flow under thevarious plenum sections areas under the waste batch is very important toensure production of high heat value quality syngas, rather than fullycombusted flue-gas. If the same flow intensity is used throughout thewhole bottom hearth plenums area through the whole operation sequencethe mixture of air and recirculated flue-gas can by-pass the waste batchby flowing from the nozzles in the chamber corners and flow around thewaste batch rather than through the batch. If this happens more fullycombusted flue-gas will be produced by excess air combustion rather thanhigh heat value syngas produced by gasification. It is also beneficialto use higher oxygen concentration and even flow distribution in allplenum areas at the end of the process of each batch to ensure fullburnout of all carbon in the waste to produce high quality ash. Thesolution provided herein allows for full control of the flow of air andrecirculated flue-gas due to the separated plenum sections and nozzleareas in the gasification chambers of the present invention.

The above mentioned control features are therefore very beneficial toachieve better production of high heat value syngas as well as producinghigh quality ash with little to no carbon content.

The syngas can be combusted in a syngas combustion chamber where thepreheated air from the gasification chamber jacket compartment(s)cooling system is used as combustion air for the combustion of thesyngas. Recirculated flue-gas diverted from the system exhaust stackductwork is also used with the combustion air such that the totalconcentration of combustion gas/air is reduced and controlled. With thisthe final oxygen concentration of the fully combusted flue-gas iscontrolled to a desired level. The reduced oxygen concentration reducesthe production of undesirable nitrogen oxides (pollutants) whichotherwise would have to be reduced with chemical treatment in the syngascombustion chamber or downstream of it. Production of nitrogen oxidesare promoted by high oxygen concentration and high temperature. Therecirculation of the flue-gas also increases the overall efficiency ofthe system. The fully combusted flue-gas from the syngas combustionchamber can be routed to an energy recovery boiler system for multiplepurposes for example to heat water for various use, steam production forindustrial use or for a conventional Rankin cycle turbine systemproducing electricity.

In an embodiment of the present invention the syngas produced is furthercooled and cleaned for the production of liquid fuel by Fischer-Tropschprocess or other gaseous fuels into liquid fuels processes.

DESCRIPTION OF DRAWINGS

The invention is further disclosed in the drawings, where the processand the components of the inventions are outlined in drawings and withtext for further explanation.

FIG. 1 is a schematic drawing of the components of a version of thesystem where the second process stage chamber is a syngas combustionchamber.

FIG. 2 shows schematically an alternative version of the system, wherethe syngas is combusted in a reciprocating engine or a gas turbine afterpassing through a syngas conditioning chamber and a syngas cleaningsystem.

FIG. 3 shows schematically an alternative version of the system, wherethe syngas is combusted directly in a boiler, reciprocating engine, gasturbine or other internal combustion device without passing through asyngas conditioning chamber or syngas cleaning system.

FIG. 4 shows a detailed view of a first process stage chamber which is agasification chamber with air/gas; fans, plenums, valves and nozzles.

FIG. 5 shows a detailed view of a first process stage chamber which is agasification chamber with air/gas; fans, plenums, valves and nozzles ina simple version with less controllability than the version shown inFIG. 4.

The following numbers have been used for identifying the differentcomponents in the drawings:

-   -   1. Gasification chamber    -   2. Syngas combustion chamber    -   3. Energy recovery boiler (steam system)    -   4. Emission control system    -   5. Power island (steam turbine generator set & condensing        equipment)    -   6. Induced draught (ID) fan    -   7. Exhaust stack    -   8. Recirculated flue-gas fan    -   9. Air fan    -   10. Cooling fluid fan for jacket cooling    -   11. Ignition burner    -   12. Valve    -   13. Syngas conditioning chamber    -   14. Syngas cleaning system    -   15. Syngas combustion in a boiler, reciprocating engine, gas        turbine or other internal combustion device    -   16. Flare stack    -   17. Thermocouple (thermometer)    -   18. Draught sensor    -   19. Pre-warming burner(s)    -   20. Jacket air vent to user    -   21. Nozzles for flow of recirculated gas and air mixture from        the plenums under the hearth to feed under the waste on top of        the hearth.    -   22. Multiple sections air plenums    -   23. Jacket cooling void    -   24. Gasification chamber bottom hearth with nozzles open from        the plenums below the hearth to the top surface of hearth (under        the waste batch)    -   25. Syngas from gasification chamber

DETAILED DESCRIPTION OF THE INVENTION

The individual components and stages of the process of the presentinvention will now be disclosed in detail.

The First Process Stage Chamber(s)

The first process stage chambers, which are the gasification chambers,are equipped with double layer casings with external cooling jacketsforming a cooling compartment (voids/channels) for the chambers coolingsystem. The chambers can be cooled by air, water, thermal oil, acombination of all or some other fluid as cooling media. The coolingsystem provides adequate cooling to the chambers walls, ceilings andbottoms.

In the case of air cooling an air fan on the gasification chamber isused to blow a controlled flow of ambient air into the external coolingjacket compartment (voids/channels) where the air cools the chambersurfaces while the air warms up. This pre-warmed air can be used ascombustion air in the case of using a syngas combustion chamber as thesecond process stage. Alternatively the air can be used for anythingwhere warm air is needed or it can be exhausted to atmosphere.

In the case of water cooling a water circulation pump is used tocirculate a controlled flow of water through the gasification chamberscooling jackets. This system can be used as an integrated part of theenergy recovery system for pre-heating boiler water or any other usewhere there is need for heated water.

Similarly other cooling fluids can be used for cooling purposes toabsorb heat in the gasification chamber cooling compartment and to makeuse of the absorbed heat elsewhere. An example of this is to use theenergy to preheat thermal oil which is used as the working media of aRankin cycle system or for industrial or space heating use.

Some of the flue-gas which is on its way to the system exhaust stack isdiverted from the stack ductwork by the recirculated flue-gas fans tothe gasification process. Each gasification chamber has a hearth withmultiple nozzles at the bottom of the chamber.

The nozzles penetrate through the hearth structure such that they form anumber of small openings between the hearth top and bottom surfaces. Thevolume under the hearth has plenums which separate the hearth nozzlesinto nozzle areas corresponding to the gas/air plenums (plenumsections). The recirculated flue-gas enters the bottom plenums via splitductwork system such that after the split a separated duct branch withits own remotely controlled valve is provided for each plenum sectionfor independent control of the recirculated flue gas flow to each plenumsection. A system with identical function is provided for atmosphericair to feed the individual plenum section with atmospheric air.

With this system of fans, valves, ducts and nozzles the gasificationprocess can as an example be started by feeding only the nozzles in thecentre of the hearth with recirculated flue gas. Then, when the bulk ofthe batch has been consumed by the gasification the outer perimeter andcorners of the hearth nozzle area are also fed with recirculatedflue-gas. At the end of the process, atmospheric air would be fed viaall nozzles in the hearth to produce quality ash with practically nocarbon content. The gasification chamber(s) are also equipped with oneor more ignition burners on each chamber.

Each gasification chamber is equipped with a duct connecting thegasification chamber to the second process stage chamber. This duct hasa valve which can be used to close the connected ductwork between thegasification chamber(s) and the second process stage chamber (syngascombustion chamber or syngas conditioning chamber or syngas manifold),therefore effectively isolating that gasification chamber from thesecond process stage chamber or manifold.

The Second Process Stage as a Syngas Combustion Chamber

The syngas combustion chamber is equipped with a variable flowcombustion air inlet. The air for this inlet can be provided by thegasification chamber(s) cooling air fan which feeds air to the externaljacket cooling system and from there to the syngas combustion chamber.

The syngas combustion chamber is equipped with recirculated flue gas fansystem where flue-gas is diverted from the system stack via ductwork andfan to the entry side of the syngas combustion chamber. By controllingthe flows of recirculated flue gas and combustion air both thetemperature and the oxygen concentration of the flue-gas from the syngascombustion chamber can be controlled.

The syngas combustion chamber is equipped with one or more auxiliaryfuel burners. These burners are used for pre-warming the syngascombustion chamber at time of system start-up. These burners are alsoautomatically ignited to maintain process temperature above set point incase of disturbance in the flow of syngas to the syngas combustionchamber.

The syngas combustion chamber can be equipped with an emergency by passstack which can be opened to vent flue-gas from the chamber from theexit end in case of equipment failure downstream of the chamber.

The Second Process Stage with a Syngas Conditioning Chamber

The syngas conditioning chamber is provided to mix the syngas flows fromthe various first process stage chambers (the gasification chambers),into a consistent mixture for further processing or combustion.

The syngas from the syngas conditioning chamber is combusted in areciprocating engine or gas turbine either directly from the syngasconditioning chamber or after additional cleaning in a syngas cleaningsystem. The quality of the syngas depends on the quality of the wastefuel or biomass processed in the system. The level of necessarypurification and/or cleaning required before combusting in areciprocating engine or gas turbine depends on the quality of thesyngas.

The syngas conditioning chamber can be equipped with an emergency flarestack which can be used to vent syngas from the chamber from the exitend in case of equipment failure down-stream of the chamber or duringstart-up or shut down of the system. The flare stack is used to burn offthe syngas, while it is not being combusted in a boiler, reciprocatingengine, gas turbine or internal combustion device. The stack can have abuilt in burner and an air inlet which is used to ensure that only fullycombusted flue-gas is emitted to atmosphere.

The Second Process Stage without a Syngas Conditioning Chamber

If the syngas has little or no impurities the syngas can be routeddirectly through a common manifold to a boiler, gas turbine,reciprocating engine or other internal combustion device.

Operation of the System of the Invention

The operation of the first process stage is practically the sameregardless if the second process stage is a syngas combustion chamber orsyngas combustion in a boiler or internal combustion device with orwithout conditioning chamber and with or without syngas cooling andcleaning. The only difference is what kind of measurement of the processrate i.e. production of useful power and/or heat is used to control therate of the syngas production. The first process stage operation willtherefore be discussed first followed by the second process stageoperation descriptions.

First Process Stage, Waste Loading, Ignition and Ash Discharge

Loading method for the system of the present invention is dependent onthe size of the gasification chambers. Loading systems can be selectfrom; front end loader, telescopic handler, overhead cranes, conveyorloading or hand loading to mention a few. The waste is typically loadedthrough a loading door on the top of the chamber. After loading thewaste into the gasification chamber(s) they are closed and sealed tight.

Following this the remotely controlled valve on the ductwork between thegasification chamber(s) and the second process stage is opened. A smallflow of gas/air mixture is then blown under the waste batch and a flamefrom an ignition burner(s) is lit for a short period of time. Theburner(s) run until the temperature of the gas flowing from thegasification chamber reaches the burners upper temperature set-point asset in the control computer program. Once this temperature is reached,the burner shuts off automatically. The gasification of the waste startsin a matter of few minutes after ignition and continues while thegas/air mixture is fed under the waste batch and there is combustiblematerial in the chamber. The rate of the gasification is governed by theflow rate of the gas/air mixture under the waste.

When all combustible materials have been consumed by the gasificationprocess the flow of gas/air mixture is closed off with the remotelycontrolled valves and the gasification chamber is isolated again fromthe rest of the system by closing the remotely controlled valve on theductwork between the gasification chamber and the second process stage.At this point the access doors can be opened to remove the ash and anynon-combustible materials there may be left from the waste. The ashdischarge method is dependent on the capacity of the system it can bedone with a telehandler, push rams, scraping system, conveyors, trolleysand by hand tools to mention a few options.

First Process Stage, Continuous Sequential Operation

FIGS. 1, 2 and 3 show four gasification chambers connected via ductworkto a common second process stage. While this 4 to 1 setup may be asuitable configuration in many cases it is by no means a fixed setting.Maintaining smooth sequential operation in a system with only twogasification chambers can be difficult although not impossible. Also, asetup with more than six gasification chambers connected via ductwork toa common second stage chamber is also difficult. Because it can betechnically complex to connect six gasification chambers to the entryend of one second process stage chamber. Therefore most systems intendedfor continuous sequential operation are designed to have 3-6 firstprocess stage chambers.

During typical operation of a 4 to 1 gasification system two to threegasification chambers would be producing syngas by gasification whichwill have progressed to different level of completion since they wouldall have been started at a different time one after another. At the sametime one chamber would possibly be just about completing its process ofcombusting any remains of carbon in the ash while another would beisolated from the rest of the system for ash discharge and reloading oralready loaded sealed and the batch load ready for ignition.

The composition and the heat value of the syngas produced in these twoto three chambers producing syngas at the same time would varysignificantly as generally the heat value of the syngas peaks sometimeafter ignition and gradually trails off until there is very little heatvalue left in the waste batch at which time the product is fullycombusted flue-gas rather than syngas. When the temperature of the gasesflowing from the chamber start to drop it is a clear indication that allcombustible elements have been consumed and it is time to stop to feedgas/air mixture to the plenums and nozzles. The control computer isprogrammed to make use of this information to stop the gas/air mixtureflow.

Following this it is time to isolate the chamber from the reminder ofthe system by closing the valve on the duct between the gasificationchamber and the syngas combustion chamber. Then the gasification chambercan be opened and ash removed and a new batch loaded into the chamber.

The chamber is fully cooled down as soon as the process is completedbecause of the jacket cooling system, therefore ensuring fast turnaroundto get the chamber ready for the next gasification cycle.

The recirculated flue-gas and air fans and the individual gas/airplenums and valves under the gasification chamber hearth sections can becontrolled in various ways depending on designers and operatorpreference, which can be varied from batch to batch by pre-programedsettings and a selection of operator options. One typical version ofthis would be controlled such that at the beginning of the gasificationcycle only the centre area of the hearth would be fed with recirculatedflue-gas, then the sides would be added when the batch has beenprocessed by half or so and at the same time higher oxygen concentrationsuch as 50/50 air and recirculated flues gas would be fed to the centreplenum. Eventually the corner sections would be opened and feed firstwith a 50/50 gas/air mixture and for a short while at the end of thecycle all plenum sections would be fed with air to ensure good burnoutof the combustible materials and high quality carbon free ash. Thesyngas temperature rises gradually over the course of the gasificationcycle in each chamber which gives an indication of how the process isprogressing, it is therefore easy to program procedures and operatoroptions into the industrial control computer to automatically controlhow the fans and valves associated with the plenums and nozzles underthe bottom hearths of the gasification chambers are controlled.

The overall flow of the gas/air mixture is controlled with a feedbacksignal from the second process stage. This signal is given by somemeasure of the production of useful power and/or heat, which is a clearindication of the corresponding process rate. These feedback signals arediscussed further in the discussion below about the second process stageprocesses. The feedback signal is used to vary the overall flow ofgas/air mixture under the waste batch and therefore the production ofsyngas.

When the gasification cycle is being started in a gasification chamberthe initial flow of gas/air mixture fed under its waste batch is startedat a pre-set level, but as soon as the process has started the automatedindustrial computer control takes over. The automated controls vary thegas/air flows under the waste batch up and down by equal amounts suchthat if the control system for example calls for an increase in theproduction of syngas which would for example call for the level of 1/10increase of the flow, the system would add 1/10 of the gas/air flowunder the waste in each chamber. Although this control feature willgently vary up and down the trend is though definitely always toincrease the flow of gas/air mixture until the chamber has run itscourse in the gasification cycle and it is isolated from the reminder ofthe system. Further, since all the active gasification chambers werestarted at different times the chambers which were started earlier willalready have higher flow setting and when the control system calls forthe additional 1/10 increase the earliest chamber may for examplealready have progressed to 7/10 setting and therefore have a resultingsetting of 8/10 while another one which was started later goes forexample from a setting of 1/10 to 2/10. With this control method thesmoothest changeover from one chamber to the next can be achieved as thechambers gasification cycle is started while at another moment a chambermay be taken off line because it has completed its cycle.

Operation with a Syngas Combustion Chamber

The syngas combustion chamber is preheated with auxiliary burners. Thecontrol system and the same burners also ensure that settable minimumtemperature is always maintained in the chamber during operation. If thetemperature in the chamber drops due any reason the burners willautomatically be started to maintain the temperature above the limit.The burners are controlled automatically with variable fuel flow andthey are shut down when not needed.

The combustion temperature in the syngas combustion chamber is adjustedto the desired temperature by controlling precisely the flow of gas/airmixture to be mixed with the syngas in the entry end of the chamberwhere the main mixing and combustion zone is. The temperature of thefully combusted flue-gas flowing from the chamber is constantly measuredby a thermocouple and the signal fed to the industrial control computerwhere an output signal is produced to control the flow of gas/airmixture to the chamber inlet end by varying the speed of fan(s) and/orposition of valve(s). An oxygen sensor is also provided to measure theoxygen concentration of the fully combusted flue-gas exiting the syngascombustion chamber. A signal from this sensor is used to control theratio of the mixture of the combustion air and recirculated flue gas byvarying the speed of fan(s) and/or position of valve(s).

The combustion air and recirculated flue gas is mixed with the syngas onthe entry end of the syngas combustion chamber. The preheated coolingair from the gasification chamber jacket cooling system can be used ascombustion air in the syngas combustion chamber. In that case thecontrol computer controls the speed and selection of each of the coolingfans and their valves.

The flue-gas from the syngas combustion chamber is essentially thecombined flow of syngas, recirculated flue-gas and the combustion airused for the combustion process in the syngas combustion chamber. Theflow of fully combusted flue-gas governs the rate of useful power and/orheat production. Some form of measure of the power and/or heat producedis therefore used as a feedback signal to the gasification process forcontrol of the syngas production. This can be:

-   -   The power output of a steam turbine generator system which is        proportional to the steam flow from the boiler, which again is        proportional to the flow of flue-gas from the syngas combustion        chamber.    -   Steam flow meter signal which is proportional to the flow of        flue-gas from the syngas combustion chamber.    -   Speed indication of ID fan which indicates the total flow of        flue-gas from the syngas combustion chamber.    -   A measure of the flow of flue-gas flowing from the syngas        combustion chamber

The syngas combustion chamber is designed with volume which is suitableto provide the maximum flow of flue-gas with at least the minimumresidence time (usually minimum 2 seconds) at a temperature above theminimum required. In order to fulfil the applicable regulatoryrequirements the maximum flow of the flue-gas from the syngas chambermay not exceed its design boundaries i.e. the flow may not be so fastthat the flue-gas does not spend at least the minimum time required inthe control volume which is the designed residence time volume of thesyngas combustion chamber. Therefore during all normal operation theflow of fully combusted flue-gas from the syngas combustion chamber isalways kept within the limitation determined by the minimum residencetime. There are no limitations as to how much below the residence timerequirements the flow can be adjusted and there is no specific technicallimitation to the minimum process rate.

The operator can choose to operate at any process rate below the limitsprovided by regulations and safe operation practice.

Start-Up of a Syngas Combustion Chamber in Systems with Induced Draught(ID) Fans

The whole gasification system and downstream equipment are kept under acontrolled level of negative pressure in relation to the surroundingatmospheric pressure. This is done by controlling the speed of theinduced draught fan (ID fan). The pressure difference between the insideof the syngas combustion chamber is measured with a draught sensor whichproduces a signal for the industrial control computer. The computer thenproduces a suitable output signal for the frequency controller of the IDfan which maintains the pressure difference to its set level.

Following this all necessary preparations are taken for start-up of theemissions control system and the energy recovery system.

When these processes have been started the burners on the syngascombustion chamber are started to warm up the syngas combustion chamberand the downstream equipment. The chamber is warmed up over some periodof time and guidance is taken from the recommended warm-up profiles ofthe recovery boiler and the insulation materials in the syngascombustion chamber.

When the syngas combustion chamber, the boiler system and the emissioncontrol system have been started and warmed up along with all of theirsupport systems the process in the gasification chambers can be startedone after the other in sequence with periodic time delay betweenstarting each chamber.

Operation, Combusting Syngas in a Boiler or an Internal CombustionDevice

Syngas from, the gasification of adequate heat value waste materials,fuels or biomass, containing little or no salts, chlorine, sulphur,acidic compounds, heavy metals or other impurities can be routeddirectly via manifold for combustion to a boiler, gas turbine,reciprocating engine or other internal combustion device withoutconditioning in a conditioning chamber. Depending on the combustiondevice the syngas may or may not need to be cooled prior to combustion.No oxygen containing gases are mixed with the syngas in the syngasmanifold.

If a syngas conditioning chamber is used as part of the second processstage the syngas from the various gasification chambers is mixed toproduce a consistent mix of syngas for further processing or combustionin a boiler, reciprocating engine, gas turbine or another internalcombustion device with or without additional purification or cleaning.No oxygen containing gases are mixed with the syngas in the syngasconditioning chamber.

Syngas containing elevated levels of impurities such as sulphurcompounds, hydrogen chloride, salts or other may need to be conditionedand/or cleaned. In such case, after the conditioning chamber the syngaswill enter a recovery boiler to cool the gas then the gas goes to awater quench vessel where multiple high pressure water nozzles willspray water to mix with the syngas and dissolve the impurities.Alternatively the syngas may be directed directly to the quenchingvessel. The moisture and droplets of water containing the impurities isremoved from the syngas in a moisture separator. The impurities areremoved from the water by neutralization and filtering. Alternatively,the syngas may be cleaned in a dry filtration process. The syngas flowson from the moisture separator or dry filtration process to a boiler,reciprocating engine, gas turbine or other internal combustion devicefor combustion or alternatively the syngas can be further processed intoliquid fuel by Fischer-Tropsch process or other processes turninggaseous fuels into liquid fuels.

To control the rate of the syngas production for these combustionprocesses the following can be used as feedback signal:

-   -   The power output of the reciprocating engine generator set,        which is proportional to the flow of syngas to the engine.    -   The power output of the gas turbine generator set, which is        proportional to the flow of syngas to the gas turbine.    -   The steam flow from the boiler that the syngas is combusted in.        The steam flow is proportional to the flow of syngas to the        boiler.

Start-Up of a Syngas Conditioning Chamber

A flare stack burner or a small by pass combustion chamber with a stackis started to ensure that no syngas escapes to atmosphere non-combustedwhen the process is started from cold. Then the syngas cleaningequipment is started if the system is so equipped. At this point theprocess in the gasification chambers can be started and as soon as theproduction is continuous and relatively stable the reciprocating engineor gas turbine can be started. When the syngas combustion in the engineor turbine has been started the flare stack can be gradually closed offand the burner shut down. Following this the syngas production rate canbe taken up to desired level of power output.

Energy Recovery Systems

In the version of the invention where the second process stage is asyngas combustion chamber the flow of superhot flue-gas is used togenerate useful energy with a recovery boiler of some sort. Manycommercially available options are suitable for this and even moredifferent versions of how these options are formed into a functioningenergy recovery system.

If electricity is the desired form of energy production from waste, fuelor biomass with the invention a common way to do so is to apply anenergy recovery boiler system to the process to produce superheatedsteam. Where the superheated steam is used in a Rankin cycle processwhere steam turbine and electricity generator set produce electricityfrom the steam with the necessary condensers, cooling towers and otherrelated equipment. Water for various usage can also be heated in asuitable recovery boiler.

Various other means can be applied for the recovery of energy from thewaste, fuel or biomass in the case of the second process stage being asyngas combustion chamber all of which rely on making use of heat in theform of superhot flue-gas at a controllable temperature and flow rate.

In the version of the invention where the second process stage is syngascombustion in an internal combustion device of some sort, the main focusis to produce quality syngas for the production of useful energy such asin a boiler, reciprocating engine or a gas turbine with or withoutfurther purification and cleaning. Alternatively useful energy recoveryfrom this version of the process is to apply the Fischer-Tropsch processor other processes which can produce liquid fuel from syngas.

General Start-Up of Systems

Before starting up the gasification in the first process stage chambersthe second process stage must be prepared and started-up. In essencemost of the overall system is started back to front considering thegasification chambers to be the front and the exhaust stack the back.Steam turbines, gas turbines and reciprocating engines are though notstarted until the process has been brought up to some stable productionof syngas.

1. A process for thermal oxidation of combustible materials comprisingthe steps of: a) gasification of combustible materials in one or moregasification chambers, b) transferring syngas from the one or moregasification chambers to a combustion unit, and c) combustion of syngasfrom the gasification chamber in the combustion unit, wherein externalair, recirculated flue-gas from the combustion unit or a mixture thereofis blown under the combustible material in separated nozzle areas of thebottom of each gasification chamber, said nozzle areas corresponding toplenum sections of the bottom of each gasification chamber, at differenttimes of a gasification cycle.
 2. The process according to claim 1,wherein the combustible materials comprise waste, fuel or biomass. 3.The process according to claim 1, wherein the combustion unit is acombustion chamber, reciprocating engine, boiler, gas turbine or aninternal combustion device.
 4. The process according to claim 1, whereina flow of fully combusted flue gas from the combustion unit is regulatedby varying the production of syngas in the one or more gasificationchambers by a feedback signal.
 5. The process according to claim 3,wherein the combustion unit is a combustion chamber.
 6. The processaccording to claim 5, wherein the feedback signal is a signal from asteam flow meter, power output measure meter, speed indicator from an IDfan, flow signal from the outlet of the combustion unit or a combinationthereof.
 7. The process according to claim 1, wherein the combustionunit is a reciprocating engine, boiler, gas turbine or an internalcombustion device.
 8. The process according to claim 7, wherein thefeedback signal is power output of the reciprocating engine generatorset, power output of the gas turbine generator set, or steam flow outputfrom the boiler that the syngas is combusted in, where the output isproportional to the flow of syngas to the respective combustion unit. 9.The process according to claim 8, wherein a syngas conditioning chamberis used as a part of the second process stage to mix the syngas from themultiple gasification chambers before it is routed to the combustionunit.
 10. The process according to claim 1, wherein the oxygenconcentration of the external air and the recirculated flue-gas in eachplenum section area is regulated independently.
 11. The processaccording to claim 1, wherein the flow of the external air and therecirculated flue-gas in each plenum section area is regulatedindependently.
 12. The process according to claim 1, wherein the overallflow of air and recirculated flue-gas to the hearth sectionscollectively is regulated.
 13. The process according to claim 1, whereinthe one or more gasification chambers are surrounded by a coolingcompartment for cooling the gasification chamber.
 14. The processaccording to claim 12, wherein air is used as cooling media in thecooling chamber.
 15. The process according to claim 12, wherein water isused as cooling media in the cooling chamber.
 16. The process accordingto claim 12, wherein thermal oil or other fluid is used as cooling mediain the cooling chamber
 17. The process according to claim 13, whereintwo or more gasification chambers are connected to the same combustionunit to provide a constant flow of syngas for combustion.
 18. Theprocess according to claim 1, wherein the mixture of external air flowand recirculated flue-gas is mixed in any ratio and introduced into thecombustion unit for the combustion of syngas.
 19. The process accordingto claim 17, wherein the external air flow introduced into thecombustion chamber is heated air from the cooling compartment of thegasification chamber.
 20. The process according to claim 4, wherein theflow of fully combusted flue gas is regulated by varying the productionof syngas in the one or more gasification chambers by a feedback signalfrom devices such as, but not limited to draught sensors, thermocouples,fan speeds indicators, steam flow meters, oxygen concentration metersand power production indicators.
 21. An apparatus for thermal oxidationof combustible materials, the apparatus comprising: one or moregasification chambers for gasification of combustible materials, the oneor more gasification chambers further comprising: a plurality inlets atthe bottom of the chamber, one or more burners, a combustion unit forcombustion of syngas from the first chamber, the second combustion unitfurther comprising; a gas inlet for receiving syngas from the one ormore gasification chambers, a burner, and an outlet for disposing offlue-gas from the combustion unit, a duct to transfer syngas from eachof the gasification chambers to the combustion unit, the duct furthercomprising a valve to isolate each of the gasification chambers from thecombustion unit, a duct for re-directing flue-gas from the outlet of thecombustion unit into the one or more gasification chambers, anindustrial computer, wherein plenums under the bottom hearth form plenumsections, wherein a plurality of nozzles penetrating the bottom hearthof each gasification chamber form the plurality of openings into thegasification chamber, said nozzles forming separated nozzle areascorresponding to the plenum sections, and wherein external air,recirculated flue-gas from the combustion unit or a mixture thereof isblown under the combustible material through the nozzles of theseparated nozzle areas at different times of a gasification cycle. 22.The apparatus according to claim 21, wherein the gasification chamber issurrounded by a cooling compartment for cooling the gasificationchamber.
 23. The apparatus according to claim 21, wherein a syngasconditioning chamber is placed between the one or more gasificationchambers and the combustion unit connected with ducts to mix the syngasfrom the one or more gasification chambers before it is routed to thecombustion unit.
 24. The apparatus according to claim 21, wherein thecombustion unit is a combustion chamber, reciprocating engine, boiler,gas turbine or an internal combustion device.